Journal Article

Inside-out or outside-in: the topology of reionization in the photon-starved regime suggested by Lyα forest data

Tirthankar Roy Choudhury, Martin G. Haehnelt and John Regan

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 2, pages 960-977
Published in print April 2009 | ISSN: 0035-8711
Published online March 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14383.x
Inside-out or outside-in: the topology of reionization in the photon-starved regime suggested by Lyα forest data

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We use a set of seminumerical simulations based on the Zel'dovich approximation, the friends-of-friends algorithm and excursion set formalism to generate reionization maps of high dynamic range with a range of assumptions regarding the distribution and luminosity of ionizing sources and the spatial distribution of sinks for the ionizing radiation. We find that ignoring the inhomogeneous spatial distribution of regions of high gas density where recombinations are important – as is often done in studies of this kind – can lead to misleading conclusions regarding the topology of reionization, especially if reionization occurs in the photon-starved regime suggested by Lyα forest data. The inhomogeneous spatial distribution of recombinations significantly reduces the mean-free path of ionizing photons and the typical size of coherently ionized regions. Reionization proceeds then much more as an outside-in process. Low-density regions far from ionizing sources become ionized before regions of high gas density not hosting sources of ionizing radiation. The spatial distribution of sinks of ionization radiation also significantly affects the shape and amplitude of the power spectrum of fluctuations of 21 cm emission. The slope of the 21 cm power spectrum as measured by upcoming 21 cm experiments should be able to distinguish to what extent the topology of reionization proceeds outside-in or inside-out, while the evolution of the amplitude of the power spectrum with increasing ionized mass fraction should be sensitive to the spatial distribution and the luminosity of ionizing sources.

Keywords: intergalactic medium; cosmology: theory; large-scale structure of Universe

Journal Article.  14047 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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